package whois

import (
	"fmt"
	"strconv"
	"strings"
	"time"
)

func parseDateAuto(s string) time.Time {
	s = strings.TrimSpace(s)
	if s == "" {
		return time.Time{}
	}

	withZoneLayouts := []string{
		time.RFC3339Nano,
		time.RFC3339,
		"2006-01-02T15:04:05.999999999-0700",
		"2006-01-02T15:04:05-0700",
		"2006-01-02 15:04:05 -0700",
		"2006-01-02 15:04:05 -07:00",
		"2006-01-02 15:04:05 MST",
		"2006/01/02 15:04:05 (MST)",
		"02-Jan-2006 15:04:05 MST",
		"02-01-2006 15:04:05 -0700",
	}
	localLayouts := []string{
		"2006-01-02T15:04:05.999999999",
		"2006-01-02T15:04:05",
		"2006-01-02 15:04:05",
		"2006-01-02",
		"2006/01/02 15:04:05",
		"2006/01/02",
		"2006.01.02 15:04:05",
		"2006.01.02",
		"02-Jan-2006",
		"02.01.2006 15:04:05",
		"02.01.2006",
		"2.1.2006 15:04:05",
		"2.1.2006",
		"02-01-2006 15:04:05",
		"02-01-2006",
		"Mon Jan 2 15:04:05 2006",
	}

	for _, candidate := range normalizeDateCandidates(s) {
		for _, l := range withZoneLayouts {
			if t, err := time.Parse(l, candidate); err == nil {
				return t.In(time.Local)
			}
		}
		for _, l := range localLayouts {
			if t, err := time.ParseInLocation(l, candidate, time.Local); err == nil {
				return t
			}
		}
	}
	return time.Time{}
}

func normalizeDateCandidates(s string) []string {
	seen := map[string]struct{}{}
	out := make([]string, 0, 6)
	push := func(v string) {
		v = strings.TrimSpace(v)
		if v == "" {
			return
		}
		if _, ok := seen[v]; ok {
			return
		}
		seen[v] = struct{}{}
		out = append(out, v)
	}

	push(s)
	push(strings.Trim(s, "\"'"))
	if i := strings.Index(s, " ("); i > 0 && strings.HasSuffix(s, ")") {
		push(s[:i])
	}
	if strings.HasSuffix(strings.ToUpper(s), " UTC") {
		push(strings.TrimSpace(s[:len(s)-4]) + " +0000")
	}
	if gmt := normalizeGMTOffsetSuffix(s); gmt != "" {
		push(gmt)
	}
	return out
}

func normalizeGMTOffsetSuffix(s string) string {
	trimmed := strings.TrimSpace(s)
	upper := strings.ToUpper(trimmed)
	idx := strings.LastIndex(upper, " GMT")
	if idx <= 0 {
		return ""
	}

	base := strings.TrimSpace(trimmed[:idx])
	offset := strings.TrimSpace(trimmed[idx+4:])
	if len(offset) < 2 {
		return ""
	}
	sign := offset[0]
	if sign != '+' && sign != '-' {
		return ""
	}
	offset = offset[1:]

	hourText := offset
	minText := "00"
	if p := strings.Index(offset, ":"); p >= 0 {
		hourText = offset[:p]
		minText = offset[p+1:]
	}
	if hourText == "" {
		return ""
	}

	hour, err := strconv.Atoi(hourText)
	if err != nil {
		return ""
	}
	mins := 0
	if minText != "" {
		mins, err = strconv.Atoi(minText)
		if err != nil {
			return ""
		}
	}
	return fmt.Sprintf("%s %c%02d%02d", base, sign, hour, mins)
}